The woman's weight must be on the ball of the foot so she can pivot as if on a fixed pin. But she does not pivot her whole body. She only pivots her lower body from the waist down. The waist is like the swivel, which joins the upper body and the lower body. Since her torso is connected to the man's torso in the embrace, she has to turn her lower body sideways in order to dance around him. This is known as “dissociation”.
It needs to be pointed out that dissociation is different from CBM (contra-body movement). CBM is turning the right side of the body towards a left moving leg or turning the left side of the body towards a right moving leg, but dissociation is the swivel of the lower body only. When practicing dissociation in front of a mirror, you should let your torso face the mirror still and rotate the hips only. You should not cheat by turning your torso instead of swiveling your hips.
A typical figure using dissociation is the ocho, in which the man leads her to draw an S on the floor with one leg, and then draw another S on the floor with the other leg. The two S's are overlapped in the opposite directions so they look like the figure 8. To dance the ocho, she needs to swivel her hips to one side of him and make a forward step, then swivel her hips to the other side of him and make another forward step, and then swivel her hips back to face the man. A similar figure using this technique is the back ocho, in which she dances the ocho backwards. She first swivels her hips and steps backwards to one side of him with one leg, then swivels her hips and steps backwards to the other side of him with the other leg. If she is able to make very big hip rotations, she can move forward by doing the back ocho and move backward by doing the front ocho. A third example using dissociation is the molinete, which is a combination of a forward step, a side step, a back step, a side step in a circular motion. In all these examples the woman keeps her chest connected to the man and rotates only her hips from one side to the other side. The technique suits the flexible body of the woman and highlights her femininity, as she turns her hips alternately while her chest remains connected to the man.
The rotation of the hips causes her torso to roll slightly on his torso, generating a pleasant sensation know as "gear effect". The chest is the center of her attention through which everything, including emotion, feeling, music interpretation, intention, seduction and flirtation, is expressed and exchanged. The woman should not glue her chest on the man's torso, but should let it roll as she swivels her hips. At each swivel, the weight of her chest is shifted to one side. As she swivels her hips to the other side, her chest rolls along until the weight is transferred to the other side.
The rolling of the chest is caused by the rotation of the hips. To create the gear effect, the woman has to swivel her hips in full until her torso rolls along. She needs to make the rolling void of abruptness and bumpiness so it feels smooth, comfortable and musical, which is not easy to do and needs a lot of practice to master. A beginner who does not know how to dissociate her upper body and lower body often keeps her hips still and crosses her leg instead. Consequently, her chest sticks on his torso and does not trundle. Tango is a dance in which both partners pleasure each other with their bodies. An experienced woman knows how to use her body to seduce the man, just like an experienced man knows how to display her feminine beauty. (See Revealing her Beauty in Tango.) Gear effect increases the sensual pleasure of the dance - a feature of close-embrace tango that is missing in the open-embrace style. It is one of the things that make the two styles fundamentally different.